Process for producing a photolithographic printing plate

ABSTRACT

IN A PROCESS FOR PRODUCING A PHOTOLITHOGRAPHIC PRINTING PLATE WHICH COMPRISES FORMING BY THE DIFFUSION TRANSFER PROCESS A REVERSAL SILVER IMAGE OF AN ORIGINAL IMAGE ON HYDROPHILIC SURFACE PORTION OF A CELLULOSE ORGANIC ACID ESTER SHEET HAVING A HYDROPHILIC SURFACE PORTION CONTAINING A SILVER HALIDE DEVELOPING NUCLEUS SUBSTANCE USED IN THE DIFFUSION TRANSFER PROCESS AND REMOVING THE HYDROPHILIC SURFACE PORTION HAVING SAID SILVER IMAGE TO EXPOSE AN OLEOPHALIC SURFACE OF SAID CELLULOSE ORGANIC ACID ESTER SHEET, THE IMPROVEMENT WHICH COMPRISES REMOVING SAID HYDROPHALIC SURFACE PORTION HAVING SAID SILVER IMAGE WITH AN AQUEOUS ETCHING SOLUTION CONTAINING A PEROXODISULFATE IS DISCLOSED.

June 4, 1974 FUMIAKI SHINOZAKI ETIAL 3,814,602

PROCESS FOR PRODUCING A PHOTOLITHOGRAPHIC PRINTING PLATE Filed July 17,1972 FIGI RELATIVE REFLECTION DENSITY OF THE PRINT 0I 0.2 AVERAGETRANSMISSION DENSITY DF DOT SCALE AFTER DEVELOPMENT OF PHOTDSENSITIVEELEMENT (I50 LINES PER INCH) United States Patent O PROCESS FORPRODUCING A PHOTOLITHO- GRAPHIC PRINTING PLATE Fumiaki Shinozaki,Tomoaki Ikeda, Yoshito Mukaida, and Masayoshi Tsuhoi, Asaka, Japan,assignors to Fuji Photo Film Co., Ltd., Minami Ashigara-shi, Kanagawa,

U.S. Cl. 96-29 L 20 Claims ABSTRACT OF THE DISCLOSURE In a process forproducing a photolithographic printing plate which comprises forming bythe difiusion transfer process a reversal silver image of an originalimage on a hydrophilic surface portion of a cellulose organic acid estersheet having a hydrophilic surface portion containing a silver halidedeveloping nucleus substance used in the diffusion transfer process andremoving the hydrophilic surface portion having said silver image toexpose an oleophilic surface of said cellulose organic acid ester sheet,the improvement which comprises removing said hydrophilic surfaceportion having said silver image with an aqueous etching solutioncontaining a peroxodisulfate is disclosed.

BACKGROUND OF THE INVENTION (1) Field of the invention The presentinvention relates to a process for producing a photolithographicprinting plate and, more particularly, to a process for producing aphotolithographic printing plate which comprises forming silver imageson an oleophilic support having a hydrophilic surface and removing thehydrophilic surface part corresponding to the silver images to exposethe oleophilic support.

(2) Description of the prior art In general, the lithographic printingplate comprises an oleophilic ink receiving area which forms an imagepart and a hydrophilic area which forms a non-image part. In producingsuch a printing plate, a method for changing the image part of thehydrophilic surface into a part having oleophilic properties and amethod which comprises providing a hydrophilic layer on a surface of anoleophilic material and exposing the oleophilic part by removing thehydrophilic layer at only the image part are known.

For example, British Patent Specification No. 1,129,366 describes aprocess for producing a printing plate which comprises using a sheetelement having a hydrophilic layer containing a nucleus substance usedfor a diffusion transfer processon a support having an oleophilicsurface, forming a silver image on the hydrophilic layer, and removingthe corresponding hydrophilic layer utilizing the silver image to exposethe oleophilic support. Further, U.S. Pat. No. 3,385,701 describes aprocess for producing a printing plate which comprises carrying outdiffusion transfer development by contacting an exposed negative elementwith a sheet element having a hydrophilic layer containing a nucleussubstance used for the diffusion transfer process on a support having anoleophilic surface to form Patented June 4, 1974 "ice a silver image,and removing the corresponding hydrophilic layer utilizing the silverimage to expose the olephilic support.

However, according to the processes described in British PatentSpecification No. 1,129,366 and U.S. Pat. No. 3,385,701, close adherenceof the surface of the support and the hydrophilic layer is notsufiicient, because the hydrophilic layer is applied to an oleophilicsurface of the support of the printing plate. Consequently, theseprocesses have the disadvantages that the hydrophilic layer of thenon-image part peels off on printing and staining is caused by adhesionof oily inks. Further, the hydrophilic layer used in these processes,which is composed of gelatin and colloidal silica does not always havesuificient hydrophilic properties, and consequently it is not possibleto obtain many printed sheets having good quality, because the oily inkadheres generally to the non-image part to cause staining as the numberof printing sheets increases.

In German Patent Publication (OLS) No. 2,048,594, a process forproducing a photolithographic printing plate by which thesedisadvantages are improved is described.

Namely, the photolithographic printing plate is produced by a methodcomprising exposing to an image of an original a photosensitive sheetwhich is prepared by applying a photosensitive silver halidephotographic emulsion to a hydrophilic surface of a cellulose organicacid ester sheet having a hydrophilic surface portion containing anucleus substance used for the diffusion transfer process, forming areversal silver image of the original on the hydrophilic surface portionby the diffusion transfer process, and removing the hydrophilic surfaceportion having the silver image by treating the hydrophilic surfaceportion with an aqueous solution containing hydrogen peroxide to exposean oleophilic surface of the cellulose organic acid ester sheet.

In this process, however, strong rubbing of the hydrophilic surface atetching so as to expose the oleophilic surface is necessary and it isdifiicult to expose the oleophilic surface completely, because thehydrophilic portion sometimes remains or is injured by the rubbing.Furthermore, if the hydrophilic surface part is thinned previously so asto be capable of exposing the oleophilic surface by rubbing softly,staining is caused easily at printing and particularly fine lines areeasily crushed.

An object of the present invention is to improve the defects of theprior processes and to provide a process for producing aphotolithographic printing plate by etching the silver image formed bythe diffusion transfer process.

SUMMARY OF THE INVENTION As the result of much research on etchingsolutions for removing the hydrophilic surface portion corresponding tothe silver image on a cellulose organic acid ester sheet so as to exposethe oleophilic part of the cellulose organic acid ester sheet, thepresent inventors have found that the above-described object can beattained by treating the sheet with an aqueous solution ofperoxodisulfate.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING The figure shows therelationship between the relative reflection density of a print and the.silver'content of the printing plates after development, in which theplates are produced using a halftone wedge and exposing to light a sheetprepared in accordance with a process-of the present invention (Curve 1)and a plate prepared in accordance with a prior art process (Curve 2).

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the presentinvention is explained in the following. A nucleus substance used forthe silver halide diffusion transfer process is incorporated in ahydrophilic surface portion of a cellulose organic acid ester sheetwhich is prepared by hydrolyzing a surface portion u'sing'alkalis oracids. To this hydrophilic surface part, a photosensitive silver halideemulsion is applied. As the photosensitive silver halide emulsion,those, such as silver chloride, silver bromide, silver bromochloride,silver chloroiodide, silver bromoiodide, silver chlorobromoiodideemulsions and those described in U.S. Pat. Nos. 3,120,795, 3,385,701 and3,020,155 and British Pat. No. 1,129,366, being used in the photographicfield generally are used preferably. Color sensitivity of the emulsionsis usually orthochromatic, but regular emulsions can be used if desired.In producing color prints from color originals, panchromaticallysensitized emulsions are used. Suitable orthochromatically andpanchromatically sensitized emulsions with dyes as described in U.S.Pat. Nos. 2,526,632 and 2,503,776 can be used. The emulsions can besubjected to metal sensitization, for example, as described in U.S. Pat.Nos. 2,448,060, 2,399,083 and 2,597,915 etc., sulfur sensitization, forexample, as described in U.S. Pat. Nos. 1,574,994, 2,410,689, etc. orreduction sensitization, for example, as described in U.S. Pat. No.2,487,- 850 etc., or can contain an antifogging agent and a surfaceactive agent. When the photosensitive sheet element is exposed throughan original or using a camera, a positive print is obtained if theoriginal is positive. The original may have line drawings or half-tonegradations. Further, it is possible to expose directly to an originalhaving halftone gradation using a screen. Exposure can be carried outeither by close contact or using enlargement. The exposed sheet elementis treated with a diffusion transfer developer such as is described inU.S. Pat. No. 3,120,795, U.S. Pat. No. 3,385,701, and British Pat. No.930,572. The developed sheet element is treated with a hot water toremove the emulsion layer. Although this step is not always necessary,it is possible to include this step in order to prevent-any undesirableetching on the hydrophilic surface portion from the silver image of theexposed portion on the emulsion layer. In another process as describedin U.S. Pat. No. 3,385,701 for forming a positive silver image on ahydrophilic surface portion of a cellulose organic acid ester sheet, thehydrophilic surface part is brought into contact with a sheet having aphotosensitive silver halide emulsion layer which has been exposed tolight in the presence of a diffusion transfer developer to form a silverimage on the hydrophilic surface portion.

The silver image obtained in such manner is treated with an etchingsolution containing a peroxosulfate or a peroxodisulfate. The ammonium,sodium, potassium, lithium, barium and strontium salts ofperoxodisulfate are preferred.

Bythis treatment, the hydrophilic surface part having the silverimagecan be removed easily.

' Although both of the above-described sulfates exhibit t esame'e'lfect, peroxodisulfate is preferable from the standpoint ofstability in solution. These can be used alone or as combinationsthereof in an amount of from 0.375% by weight'to 30% by weight based onthe weight of the treating solution;

kinder to. accelerate the etching function, at least one of a cupricsalt, an acid or a substance which forms a complex having, a lowsolubility byreacting with the silver is added to the etching solution,i.e., a substance whose silversalt has a low solubility. As the cupricsalt, water soluble cupric saltssuch as cupric chloride, cupric bromide,cupric nitrate, cupric sulfate and cupric citrate are suitable, with thecupric halides being particularly 4 preferred. Suitable acids which canbe used are organic acids such as acetic acid, citric acid, tartaricacid, fumaric acid, maleic acid and benzene sulfonic acid etc. andinorganic acids such as hydrochloric acid, nitric acid, sulfuric acidand phosphoric acid.

As the substance which forms a complex having low solubility by reactingwith silver, for example, a solubility product less than 2 -10- thewater soluble halides (chlorides, bromides, iodides) tartarates,carbonates, chromates, oxalates, thiocyanates, sulfides, and formates,can be used. The ammonium, sodium, potassium, lithium, barium andstrontium salts of these materials are preferred. The halides are alsopreferred.

These accelerating agents can be usedalone or as mixtures thereof in anamount of from 0.05 to 50% by weight based on the weight of the treatingsolution (although some compounds have a solubility less than 50% byweight, they can be used if the solubility is at least 0.05% by weight).

'Where the peroxodisulfate is used together with at least one of acupric salt, an acid or a substance which forms a complex having lowsolubility by reacting with silver, the amount of the peroxodisulfatecan range from 0.0125 to 30% by weight based on the weight of thetreating solution calculated as ammonium peroxodisulfate.

A preferred amount of the peroxodisulfate is from 0.1 to 20% by weightcalculated as ammonium peroxodisulfate based on considerations of thestability of the etching solution with the lapse of time and'thestability to the photosensitive material to be treated. Under suchconditions, the areas adjacent the silver image are etched Within 30seconds at 5 C. to 40 C. and the cellulose and the derivatives thereofare deteriorated.

When the surface of the sheet element subjected to the etching treatmentis rubbed softly, the hydrophilic surface portion is removed easily incomparison with that treated with hydrogen peroxide, by which theoleophilic surface of the cellulose sheet appears, while the remaininghydrophilic surface portion remains as it is. The printing plateproduced by such manner can be used directly or as an offset printingplate in conventionally known methods. From the printing plate of thepresent invention, more than 20,000 sheets of stable prints having goodquality can be produced using commercially available printing inks and awetting solution. In treating with an aqueous solution containingperoxodisulfate, the following advantages in comparison with the case oftreating with hydrogen peroxide are obtained. When the sheet is exposedproperly using the same continuous gradation wedge, inks adhere well onthe hydrophilic surface portion in comparison with the case of treatingwith-hydrogen peroxide, even though the quantity of silver is verysmall. Accordingly, it is possible to decrease the quantity of silverhalide in the negative emulsion layer which is animportant factor of thecost in the preparation of the photosensitive sheet, and consequently alowering of the cost of the preparation of the photosensitive sheet canbe expected. Moreover, when the sheet is exposed properly .using thesame half-tone gradation wedge,,printing of the highlights parts can becarried out correctly, and consequently small dots can be printedclearly in comparison with the case of treating with hydrogen peroxide,since thediffenence between the hydrophilic surface and the oleophilicsurface is distinct. This is a particularly important aspect in theprinting of a half-tone original, by which more preferable prints can beproduced in comparison with the case of treating with hydrogen peroxide.

Suitable cellulose organic acid esters which can be used as the sheetmaterial in the present invention include cellulose acetate, cellulosediacetate, cellulose triacetate, cellulose propionate, cellulosebutyrate, cellulose acetate propionate and cellulose acetate butyrate,etc. These cel lulose ester sheets are treated to provide a hydrophilicproperty to their surface by hydrolyzing the surface part of the sheetwith an aqueous solution of a caustic alkali such as sodium hydroxide orpotassium hydroxide, an aqueous solution of an acid such as acetic acidor a treating solution prepared by adding a polar organic solvent suchas methanol and ethanol to the above-described aqueous solutions. Anucleus substance used for the diffusion transfer process as disclosedin U.S. Pat. Nos.

2,774,667, 2,698,445, 2,698,237, 2,823,122, 2,698,238, etc. isincorporated into this hydrophilic surface portion. Asthe nucleussubstance those used commonly in the diffusion transfer process, forexample, colloidal heavy metals such as colloidal'silver and sulfurcompounds of heavy metals such as silver sulfide and nickel sulfide canbe and are preferably used. The nucleus substance can be incorporated inthe hydrophilic surface portion of the cellulose ester sheet aftersurface hydrolysis or simultaneously with surface hydrolysis.Alternatively the nucleus substance can be added previously in thepreparation of the sheet, which is then treated so as to have a surfacehydrophilic properly.

When dimensional stability or mechanical strength is required in thesheet element comprising the cellulose organic acid ester used in thepresent invention, the sheet element can be backed with a polyethyleneterephthalate film or a metal plate such as aluminum plate as a support.For example, a sheet element which is prepared by applying a subbinglayer and a layer of a cellulose organic acid ester on the subbing layercan be used.

Further, in order to form a silver image portion the hydrophilic surfacepart, a process comprising putting on diffusion transfer paper may beused.

The present invention is explained in greater detail by the followingexamples.

EXAMPLE 1 A triacetyl cellulose film having a thickness of 135g wasdipped in the following treating solution at 35 C. for 50 seconds toform a hydrophilic surface thereon by hydrolyzing the surface thereofand simultaneously to incorporate a nucleus substance used for thediffusion transfer process. The film was washed with water and dried.The above used treating solution was prepared by reacting 0.034 g. ofnickel nitrate with 5.27 g. of ammonium polysulfide in 53.3 g. ofglycerol to produce a nickel sulfide colloidal solution and dilutingthis colloidal solution with a solution having the followingcomposition.

Water ml 950 Sodium hydroxide g 200 Methanol ml 1000 Composition of thedeveloper:

Water. ml 750 "p-Methylaminophenol sulfate g 5 Anhydrous sodium sulfiteg 65 Hydroquinone g 15 .Anhydrous sodium thiosulfate g 15 Sodiumhydroxide g 20 Water to make 1000 ml.

The sheet element was dipped in warm water at 40 C. toremove theemulsion layer and dipped then for 30 seconds in an etching solutionprepared by mixing equivalent amounts of Solution Ia and Solution IIahaving the following compositions at 25 C.

Solution Ia: Cupric chloride (dihydrate) l0 Citric acid V Water to make1000 ml.

By this treatment, the positive silver image of the original formed onthe hydrophilic'surface portion of the cellulose sheet was bleached andthe image portion was etched. Then the'sheet element was rubberasoftlyusing a cotton swab or'a sponge, by which the hydrophilic portion of thesilver image was removed and the oleophilic surface of the triacetylcellulose was exposed. The resulting printing plate was placed on aconventional offset printing machine. When printing was carried outusing a commerciallly available printing ink and a wetting solution,more than 20,000 sheets of prints having good quality were produced.

On the other hand, for the purposes of comparison, the same treatmentwas carried out with using the same sheet element, the same developerand the same treating solution, but equimolar amounts of hydrogenperoxide instead of ammonium peroxodisulfate in the above-describedtreating solution were used.

Where the ink density (minimum density) of the print obtained using theprinting plate prepared by the present invention was equal to thatobtained by the comparison method, the transmission density just afterdevelopment of the photosensitive sheet was 0.25 for the sheet elementof the present invention and 0.75 for the comparison sheet element. Itcan be seen from this result that faithful printing can be carried outusing a lesser amount of silver halide according to the process of thepresent invention.

When the same procedure was repeated using a halftone scale, the resultsshown in the figure were obtained.

Namely, the figure, in which 1 represents the process of the presentinvention and 2 represents the case of the process using hydrogenperoxide shows that 1 always gives a. high reflection density (of theprint) in comparison with 2 and reproduces faithfully even though atless than a transmission density of 0.06 (high-light portions), but 2cannot express the highlight part.

EXAMPLE 2 A photosensitive sheet produced using the same conditions asdescribed in Example 1 was treated in the same manner as described inExample 1. However, a solution prepared by mixing equivalent amounts ofSolution Ib and Solution IIb having the following compositions was usedas the etching solution.

Solution Ib: G. Cupric chloride (dihydrate) 10 Tartaric acid 10 Water tomake 1 liter.

Solution 11b:

Potassium peroxodisulfate Water to make 1 liter.

By carrying out the same procedure as in Example 1, prints having goodquality were obtained.

EXAMPLE 3 A photosensitive sheet produced using the same conditions asdescribed in Example 1 was treated in the same manner as described inExample 1. However, a solution prepared by mixing equivalent amounts ofSolution- Ic and Solution IIc having the following compositions was usedas the etching solution.

Solution Ic: G. Cupric sulfate (pentahydrate) 40 Citric acid Potassiumbromide 10 Water to make '1 liter.

Solution IIc:

Ammonium peroxodisulfate I 120 Water to make 1 liter.

By carrying out. the same procedure as described in Example 1, printshaving good quality were obtained.

v a 'EXAMP'LE'4' I V i A silvn-halide photosensitive element exposed tolight through a positive original was laid on atriacetyl cellulose sheetcontaining a nucleus substance for the diffusion transfer process whichwas incorporated into the Solution Id: G. Cupric sulfate (pentahydrate)25.0 Sodium potassium tartarate 9.0

Potassium bromide 20.0 Water to make 1 liter.

Solution IIc:

Ammonium peroxodisulfate 50 Water to make 1 liter.

By this etching treatment, the hydrophilic surface portions near thesilver image formed on the hydrophilic surface portion of the triacetylcellulose sheet were removed by etching to expose the oleophilicsurface. Thus, an offset lithographic plate was obtained. This printingplate was placed on a conventional offset printing machine and printingwas carried out with using a commercially available printing ink and awetting solution, by which more than 8000 sheets of stable prints havinggood quality were obtained.

EXAMPLE 5 V A subbing layer was applied to a polyethylene terephthalatefilm having a thickness of 135 To this layer, a triacetyl cellulose wasapplied so as to have a thickness of 10 Using this sheet element, thesame procedure as described in Example 1 was carried out, by whichprints having good quality were obtained.

EXAMPLE 7 Prints having good quality were obtained using the sameprocedure as described in Example 3 but using a cellulose acetatebutyrate film (Type 161-40 produced by the Eastman Kodak Co.) instead ofthe triacetyl cellulose film. I g

EXAMPLE 8 A subbing layer was applied to a polyethylene tereph thalatefilm having a thickness of 13511.. To this film,

triacetyl cellulose containing silver sulfide dispersed therein wasapplied so as to have a thickness of 8 The sheet element was hydrolyzedat 40 C. for seconds using a solution composed of 1000 ml. of water,200g. of sodium hydroxide; and 1000 of methanol; Using this sheetelement,'the same procedure as described in Example 1 was carried out,by which prints having good quality were obtained.

Whilethe' invention has been describedin detail and in terms of specificembodiments thereof it will be apparent that various changes vandmodifications can be. made ztherein without departing from the, spiritand :scope What-is claimed-is: I v

- 1. Ina process for producing a photolithographic print- .ing platewhich comprises forming bythe'ditfusion transferv pro cess a reversalsilvcrimage of an original image on a hydrophilic surface portionlof 'a,cellulose organic acid estersheet having ahydrophilic surface portioncontaining a silver halide developing, nucleus substance used in thediffusion transfer process and removing the hydrophilic surface portionhaving said silver image to expose an oleophilic surface of saidcellulose organic acid ester sheet, the improvement which comprisesremoving said hydrophilic surface portion having said silver image withan aqueous etching solution containing a peroxodisulfate and anaccelerator selected from the group consisting of a cupric salt, an acidor a silver-complex forming sub.-

stance.

2. The process of claim 1, wherein said peroxodisulfate is selected fromthe group consisting of ammonium peroxodisulfate, potassiumperoxodisulfate, sodium peroxodisulfate, lithium peroxodisulfate, bariumperoxodisulfate and strontium peroxodisulfate.

3. The process of claim' 1, wherein said cupric salt is cupric chloride,cupric bromide, cupric nitrate, cupric sulfate or cupric citrate.

4. The process of claim 1, wherein said acid is acetic acid, citricacid, tartaric acid,.fumaric acid, maleic acid, benzene sulfonic acid,hydrochloric acid, nitric acid, sulfuric acid or phosphoric acid.

5. The process of claim 1, wherein said silver-complex forming substanceis awater soluble salt selected from the group consisting of chloride,bromide, iodide, tartarate, carbonate, chromate, oxalate, thiocyanate,sulfide and formate.

6. The process of claim 1, whereinsaid cellulose organic acid estersheetis cellulose-acetate, .c'ellulose diacetate, cellulosetriacetate,cellulose propionate,.cellulose butyrate, cellulose acetate propionateor cellulose acetate butyrate. I 7

7. The process of claim 6, wherein said cellulose organic acid estersheet is cellulose diacetate or cellulose triacetate. I g Y 8. Theprocess of claim 1, wherein said peroxodisulfat e is present in anamount of from 0.375% by weight to 30% by weight based on the Weight ofthe etching solution.

9. The process of claim 1, wherein said cupric salt is a water solublecupric salt. '1 V 10. The process of claim a cupric halide.

11. The process of claim l, wherein said silver complex formingsubstance reacts with silver "to form a'p roduct whose solubility isless than '2Xl0" a 12. The process of claim 1, whereinsaidaccelerator ispresent in an amount of from 0.05 to 50%. by Weight based on the weightof the'treating' solution. r j i v 13. The-process of claim 1," wlier'ein"said p'eroxodisulfate is present in an amount'of from 0.012510 30% byweight based on'the weight of'the etchingsolution', calculated asammonium peroxodisulfate.

14. Theprocessof claim 13, whe rein: s'aid peroxodisulfate is present inan amount o'f-from 0.1fto 20% by weight based on the weight ofthe'etc'hing solution, calculated as ammonium peroxodisulfate.

15. The process of claim 1, wherein said removing at said" hydrophilicsurface portion is'iperfornied at 5 'C;' to 40 C. within-30 seconds. k HY 16. The process of claim 1, wherein said accelerator-is said cupricsalt and said acid. H j v 17. The process of claim 1, whereinsaidI'accelera'tor fis' saidcupridsalt." 1

ISL'The'processof claim ,1, wherein said accelerator is said acid.

1, wherein said cupric salt is 9 10 19. The process of claim 1, whereinsaid accelerator 3,373,114 3/ 1968 Grunwald 252-100 is saidsilver-complex forming substance. 3,634,262 1/1972 Grunwald 134-42 20.The process of claim 5, wherein said water soluble 2,428,804 10/1947Drexel 252-100 salt is a compoimd selecteci from tile grout consistingof FOREIGN PATENTS ammoruum, sodium, potassium, lithium, barium andstron- 5 tium Sa1tS 1,186,745 1/1962 Germany.

References Cited UNITED STATES PATENTS 3,260,198 7/ 19 6-6 Wagernans9629 L RONALD SMITH, Primary Examiner I. L. GOODROW, Assistant Examiner

